The mechanism of bone loss is not completely understood, but bone loss disorders arise from an imbalance in the formation of new healthy bone and the resorption of old bone, skewed toward a net loss of bone tissue. This bone loss involves a decrease in both mineral content and protein matrix components of the bone. Ultimately, such bone loss leads to an increased fracture rate of, predominantly, femoral bones and bones in the forearm and vertebrae. These fractures, in turn, lead to an increase in general morbidity, a marked loss of stature and mobility, and, in many cases, an increase in mortality resulting from complications.
Bone loss occurs in a wide range of subjects, including post-menopausal women, patients who have undergone hysterectomy, patients who are undergoing or have undergone long-term administration of corticosteroids, patients suffering from Cushing's syndrome, and patients having gonadal dysgenesis. The need for bone repair or replacement also arises locally in the case of bone fracture, non-union, defect, prosthesis implantation, and the like. Further, such need also arises in cases of systemic bone diseases, as in osteoporosis, osteoarthritis, Paget's disease, osteomalacia, osteohalisteresis, multiple myeloma and other forms of cancer and the like.